The city's security chief was in the car when the blast went off in a neighbourhood that is a stronghold for the Mahdi Army

There were no major injuries reported.

The blast comes after Nuri al-Maliki, Iraq's prime minister, hailed a week-long military assault against Shia fighters in Basra as a "success".

Call for release

Meanwhile, Reporters Without Borders (RWB), a Paris-based media monitoring group, has called for the release of Ahmed Mahmud Hassan, a journalist for Al-Sumariya satellite television channel.

The organisation claims that Hassan was arrested on March 30 in Mahmudiyah, 30km south of Baghdad, "while covering clashes between Iraqi forces and rebel insurgents".

The journalist is thought to be detained at a military base, RWB has said.

According to the Iraqi Journalists Freedom Observatory (JFO), which monitors violence against the media, 233 Iraqi and foreign journalists and media workers have been killed in Iraq since the US-led invasion of March 2003.